The invention relates to a pump, in particular an oil pump for internal combustion engines comprising a gear assembly or a rotor assembly, each having a pressure and a suction region arranged in a pump housing. The pressure and suction regions are insulated from each other with the help of an axially displaceable control piston that limits/defines a supply chamber and a housing cover that closes the pump housing. The pressure region has a pressure channel that is connected to the waist of the control piston.
The development of automobiles with low fuel consumption presupposes the optimization of vehicle and engine components. For the fuel consumption of automobiles in frequently encountered short stretches of dense traffic and city traffic, of particular significance are the losses that are conditioned among other things by the drive of supplementary systems. The drive efficiency of among others, oil pumps that ensure lubrication of the engine, can actually lead to a lowering of engine efficiency, causing the fuel consumption to increase sharply.
Up to xe2x88x9240xc2x0 C., the function of engine lubrication, and sufficiently fast engine lubrication must be ensured. And in hot idle run operation up to 160xc2x0 C., the oil supply must be totally fault-proof. The hot idle run operation is characterized by high inner leakages in the oil pump and a relatively high oil requirement of the engine. The hot idle run operation is an essential operational point for fixing the dimensions of the oil pump.
In general, in the classical pump design, the oil pump is most suitable for this operational point. In normal vehicle operation, this leads to an oversized oil pump, because the oil feed characteristic curve runs digressively in relation to the vehicle speed. The consequence is that the supply characteristic curve of the oil pump climbs almost in linear proportion to the speed.
The excess supply of oil resulting there from is blown out through an excess pressure-regulating valve, in a manner that consumes more energy. From DE A 196 46 359, we have knowledge about a lubrication pump controlled through volumetric efficiency, that enables an improved matching of the supply characteristic curve of the oil pump with the oil feed characteristic curve of the internal combustion engine. When the threshold pressure is exceeded in the pressure region, a control piston pre-tensioned through the pressure spring, which separates the pressure region and the suction region from each other, is displaced in the rear direction, thus creating an axial play. The axial play enables a pressure balancing from the pressure region to the suction region. This way, there is a reduction in the supply volume and the pressure, so that the supply characteristic curve of the oil pump comes closer to the oil feed characteristic curve of the engine.
The task of the invention is to design a pump that enables a more precise matching of the supply characteristic curve with the oil feed characteristic curve of the engine. With increasing speed in particular, the pressure and the volumetric flow of the pump are kept near constant from a regulation point. In addition, the pump should also have a lower intake.
The problem is resolved by the invention in that the control piston works in tandem with a plunger arranged at the control piston end facing the supply chamber. The plunger is aligned at right angles to the control piston. The plunger is pre tensioned against the control piston with the help of a pressure spring. The control piston and the plunger are connected through a sliding surface aligned at an angle to the control piston axis.
An advantage of the invention is that the oblique surface enables the pre-specification of a certain path/distance ratio between the control piston and the plunger. The pressure and supply volumes of the pump increase up to the regulation point almost in a linear relation. From a threshold speed of the regulation point onwards, it is desirable that the pressure and supply volumes remain near constant in relation to speed.
Other advantages of the pump conforming to the invention are that the pulsation is reduced, and less frothing of the medium, especially of the oil takes place.
In the pump conforming to the invention therefore, there is a provision that the regulation point of the pump can be adjusted through the pre-tensioned pressure spring of the plunger. When the threshold speed is exceeded, the threshold pressure is also exceeded, so that the pressure from the pressure region forces the supply medium to impact against the waist of the control piston through the pressure regulation channel, causing the control piston to move in the backward direction against the pressure spring. The rear movement of the control spring increases the axial play.
Simultaneously, the housing cover has a pressure channel that connects the pressure region and the supply chamber. Pressure is applied on the supply chamber in a controlled manner through the pressure channel built in the housing cover. This way, the supply chamber filled earlier in the suction region is replaced with supply medium in a controlled manner from the pressure region through the pressure channel, and the excess supply medium can flow back into the suction region through the enlarged axial play, i.e., through a withdrawal of the control piston, or remain in the suction region. Additionally, the supply medium can flow back directly through the enlarged axial play from the pressure region to the suction region.
This way, the efficiency of the pump is simultaneously reduced so that the pressure and volume flows remain constant. The precondition is that the displacement of the control piston, which corresponds to the enlargement of the axial play, should have a certain relationship to the reduction of pump efficiency. The rear displacement of the control pump should be bigger than the length of the pressure spring, so that pressure and volume flows from the regulation point can be kept constant.
The control piston has an oblique surface aligned at an angle of 30xc2x0 to the control piston axis. Similarly, the plunger has an oblique surface aligned at an angle of 60xc2x0 to the axis of the plunger. Thus, a displacement ratio of 2:1 can be established. It is meaningful and expedient, if the angle xcex1 between the oblique surface of the control piston and the control piston axis has a value of 10xc2x0 to 80xc2x0, and the angle xcex2 between the oblique surface of the plunger and the plunger axis corresponds to 90xc2x0xe2x88x92xcex1. It is possible to achieve a convenient displacement ratio through a corresponding expansion of the oblique orientation of the control piston and the plunger, leading to a matched control characteristic of the pump.
A preferred embodiment of the invention has the provision that the sliding surface is designed as a curve. A further improvement in the control characteristic is achieved through a suitable design of the curve. For example, the surface of the control piston can be designed as convex so that with increasing speed, an over proportional enlargement of the axial play takes place, and hence, the supply characteristic curve can be matched optimally to the oil feed characteristic curve.
In a preferred embodiment of a pump conforming to the invention, there is the provision that the end of the control piston facing the supply chamber impacts against a spring with a non-linear characteristic curve. It is expedient, if the spring has a digressive characteristic curve. While a cylindrical pressure spring has a progressively climbing characteristic curve, the use of a spring with non-linear spring characteristic curve, particularly a digressive spring characteristic curve can improve the enlargement of the axial play in relation to increasing speed, and thus, in relation to increasing pressure.
In a preferred embodiment of a pump conforming to the invention, the spring is designed as feather spring or plate spring. The range of design possibilities for the feather spring is so large that an exact matching of the control characteristic is possible.
A further advantage is that the use of a feather spring or a plate spring permits a flat and ergonomic structure of the pump. Other types of springs that have a similar characteristic curve can also be used.
In a preferred embodiment of the invention, the control piston has a ring groove. In its withdrawn position, the control piston is connected to bypass channels that originate from the pressure region and the suction region. The bypass is closed in the initial position of the control piston. When the threshold pressure is exceeded, the control piston moves backwards. For a definite period, the ring groove on the surface of the control piston is in connection with the bypass channels originating from the pressure region and the suction region, so that the supply medium can flow back from the pressure region to the low-pressure region, i.e. to the suction region without any hindrance. This way, the volumetric efficiency of the pump can be reduced in a controlled manner additionally.
In a preferred embodiment of the invention, the housing cover has a pressure channel that connects the pressure region to the supply chamber. Pressure can be applied in a controlled manner on the supply chamber through the pressure channel in the pump cover. The pressure channel connects the pressure region with the supply chamber, so that the supply chamber is filled partly with supply medium from the pressure region. When the axial play is enlarged, or when the control piston moves back, the supply medium can flow back into the suction region, or it stays in the suction region
This means that only that much supply medium is pumped as is required by the oil feed characteristic curve of the engine.
In a preferred embodiment of the invention, the pressure channel that connects the pressure region to the supply chamber can be blocked or regulated. For example, the pressure channel remains closed up to a certain speed and opens fully or partially only to enable a pressure balancing from the pressure region to the suction region.
Further, the pressure regulation channel is also designed in such a way that it can be blocked or regulated.
In a preferred embodiment of the invention, the control piston has a wear proof surface. In particular, the sealing surface of the control piston facing the supply chamber is exposed to very high wear and tear. This results in an undesirable efficiency reduction for sealing bars of conventional pumps. The spring pressure of the plunger presses the control piston lightly, leading to a complete compensation/balancing.
In a preferred embodiment of the invention, each side of the gear assembly or the rotor assembly is provided with a control piston. The use of the second control piston on the side opposite to the first control piston enables a further improvement in the regulation of the pump. This is because the second control piston can be equipped with a spring that has a different characteristic curve than the spring of the first control piston. Further, it is possible to equip the second control piston with a spring that becomes effective only after the regulation point.
A further advantageous solution to the problem is achieved through a preferred embodiment of a pump, particularly an oil pump for internal combustion engines with a gear assembly or a rotor assembly, each comprising a pressure region and a suction region arranged in a pump housing. The pressure region and the suction region can be sealed from each other firmly with the help of a radially displaceable sliding block that limits/defines a supply chamber, and a housing cover that closes the pump housing. The pressure region has a pressure channel that is connected to the waist of the hydraulic piston. The hydraulic piston works in tandem with a sliding block at the end of the hydraulic piston facing the supply chamber, and the hydraulic piston is pre tensioned through a pressure spring.
It is possible to provide the improvement possibilities of the control characteristic also for regulating the hydraulic piston.
Further, it is possible to regulate the displacement of the control piston through a translator/actuator, so that, for example, these can be regulated with the help of a pressure sensor or volume flow measuring instrument, and thus enable the displacement of the control piston as a function of the determined measurement values. The regulation can, for example, be integrated in the engine management or in the gear regulation. The advantage is that the regulation of the supply volume through characteristic curves can be matched precisely to the concerned demand of the consumer of the pump. Examples for translators/actuators are electric servo drives (engine, gear and position measurement with feedback to the regulation), electro magnetic drives, Piezo crystal actuators, thermal actuators, hydraulic adjustable pistons and pneumatic cylinders.
The plunger can be aligned to the control piston at a suitable angle. A correspondingly adapted surface is necessary here.
Pumps conforming to the invention include among othersxe2x80x94rotor pumps, toothed rotor assembly pumps, spur wheel pumps, sickle/crescent cell pumps and winged cell pumps.
The regulation system conforming to the invention can also be used to regulate a hydro engine.